This invention relates generally to communications systems and in particular to transmitting ATM (Asynchronous Transfer Mode) cells over ADSL (Asymmetric Digital Subscriber Line).
ADSL is a newly standardized transmission technology facilitating simultaneous use of normal telephone services, one-way data transmission of six of up to eight (8) Mbits/s in the downstream and full duplex data transmission at up to 800 Kbits/s in the upstream channel. ADSL can be seen as a FDM (Frequency-Division Multiplexing) system in which the available bandwidth of a single copper-loop is divided into three parts. Passive filters are used to split POTS (Plain Ordinary Telephone Service) from the data channels to guarantee POTS service in case of ADSL system failure.
The decomposed and routed data from the access module is connected to an ATU-C (ADSL Transceiver Unitxe2x80x94Central Office) where the data is converted into analog signals. The analog signals are then carried with the POTS signals to the remote end. The ATU-C also receives and decodes data coming from customers premises send by ATU-R (ADSL Transceiver Unitxe2x80x94Remote Terminal).
Currently the ADSL standard specifies one path for all traffic. However, different traffic types (i.e., video traffic) requires faster processing than other traffic (i.e., data and e-mail). This could be interpreted as requiring two physical interfaces on the ADSL modem. Having two physical interfaces, however, increases the number of pins needed to support traffic, i.e., ATM traffic, over ADSL and thus potentially increases the complexity and expense of the implementation.
What is needed is a straightforward method to determine which latency path a particular data cell uses.
A method and system for controlling data latency in a communication network use a pre-selected portion of the data to identify one of at least two latency paths. The data is transported to a network device 500 through physical channel 502. The network device 500 includes at least two latency paths 506,508 each operable to transport the data through to other parts of the device 500 at an associated rate. In one aspect of the invention, data sorter 504 extracts a latency path identifier from the incoming data then provides the incoming data to the identified one of the at least two latency paths 506,508 accordingly. In another aspect of the present invention, the data sorter 504 extracts from the incoming data an indicator which characterizes the incoming data, decodes the characteristic indicator to determine which of the at least two latency paths 506,508 to select, then provides the incoming data to the selected one of the at least two latency paths 506,508. An interleaving device 510 may be included in a selected one of the data paths 512. The at least two latency paths 506, 508 transport the data to multiplexer 514 where the data is recombined for further transport to other portions of the device 500 through path 516.
These and other features of the invention that will be apparent to those skilled in the art from the following detailed description of the invention, taken together with the accompanying drawings.